⁸ Uguccione affirms that balbus and burrus are synonym under the lemma balo:

Balo, -as, verbum neutrum, et est ovium. Inde hic balatus et balbus, qui verba non explicat potius est videtur balare quam loqui. [...] Item a balo, burrus, id est balbus [...]. Vel dicitur blesus quasi fresus , qui verba frangit.

Balo is a neuter verb and pertains to the sound of sheep. Thus bleating and stuttering; and the person who doesn't express the words clearly is seen as bleating rather than talking. [...] Also from balo we have burrus, that is to stammer. Blesus in fact is like fresus, or a person who breaks up words into pieces.